Security camera image correction system and method

ABSTRACT

A security camera and an image, within the camera&#39;s field of view, of a test pattern, containing color elements and grayscale elements having know predetermined spectrophotometrical values and resolution elements. After taking of images at a scene, and when subsequently reproduced accurately the elements will produce electronic signals that are detectable on measuring equipment well-known to the trade, such as vectorscopes and waveform monitors. Adjustments and corrections can then be made to the images of a scene, based on those readings. A method of adjusting and correcting images using the test pattern is also disclosed.

FIELD OF THE INVENTION

A system and method that enables images previously recorded by camerasused in security, law-enforcement, medicine and other disciplines, to besubsequently standardized for image quality to enhance accuracy ofreproduction.

BACKGROUND OF THE INVENTION

While methods of controlling image quality are well-established intelevision and motion pictures, the requirements of these industriesdiffer significantly to those of law-enforcement and security.

In the entertainment world, the emphasis is on image consistency, andattractive appearance and not on accuracy of reproduction. In reality,the broadcasting and motion picture industries go out of their way toproduce images that are larger than life, because viewers preferbrighter, more colorful images.

In security and real-life image reproduction, the need is not to produceattractive pictures, but accurate reproduction of a scene or person.This is the challenge that this invention is designed to address.

While these fundamental differences exist in the requirements forrecording of images produced for entertainment, compared with thesubsequent enhancement of images already recorded in security and otherreal-life applications, there are two areas of similarity.

Image quality can be controlled either by:

Adjusting a camera's taking characteristics prior to its assignment to aproduction or location, or

Correcting the recorded images produced by the camera, in a subsequentoperation

In entertainment—camera adjustment, typically happens under controlled,often laboratory conditions where the type of lighting, spectraldistribution of the light source and brightness are carefullycontrolled.

Because such cameras have been well adjusted in the laboratory and thelighting on the set is similar to that used in the laboratory, furtheror subsequent adjustment of a recorded image is often not required.

In security and real-life situations—camera adjustment is limited.Cameras used in these applications are relatively inexpensive andinvariably have little or no image adjustment capability. Often, theonly control is to test different makes and models of cameras, and toselect those which are best suited for the task or location in whichthey will be used.

Because camera adjustment is so limited, subsequent correction ofrecorded images becomes the only option. However, this is difficult forthree reasons.

1) The cameras and lenses are relatively inexpensive, consequentlyproduce poorer quality images.

2) Achieving accurate reproduction is more difficult than producingpleasing looking pictures.

3) Lighting of the scenes being photographed is uncontrolled,inconsistent, and will vary widely at different times of day, or night,and will typically be of poor spectral quality.

The System.

To overcome these issues, this invention proposes to install within thecamera's field of view a test pattern. The test pattern may includeprecision colours, and spectrophotometrically neutral grayscale andresolution information. When reproduced accurately the colors andgrayscales of the test pattern will produce electronic signals atprescribed locations on measuring equipment well-known to the trade,such as vectorscopes and waveform monitors.

Image Correction.

When viewed on standard monitoring equipment, the images produced by thetypical cameras in question, invariably exhibit inaccurate color andgrayscale reproduction. However, using one of a number of imagingsoftware packages well-known to the trade, the color and grayscaleinformation of the recorded images can be adjusted for accuratereproduction by reference to the recorded image of the test pattern,taken at the same time and place. Because the test pattern isilluminated by the same light source as the rest of the scene, adjustingthe test pattern for accurate reproduction automatically corrects thetotal scene.

Because test patterns change with age the preferred embodiment wouldinclude a recommended replacement date within the active area of thepattern.

In another embodiment the significant test pattern information would bedisguised in graphics such as public service announcements or evencommercial advertisements. Typical Installation locations would includeairports, banks, public buildings, highways, hospital operating rooms,vehicles such as taxicabs, aircraft, buses and subways, retail stores,intersections, ad casinos and in fact anywhere security or accurateimage reproduction are important.

The various features of novelty which characterize the invention arepointed out with more particularity in the claims annexed to and forminga part of this disclosure.

For a better understanding of the invention, its operating advantagesand specific objectives attained by its use, reference should be made tothe accompanying drawings and descriptive matter in which there areillustrated and described preferred embodiments of the invention.

IN THE DRAWINGS

FIG. 1 is a schematic side view of a passenger vehicle such as a bus,showing the installation of a system illustrating the invention, with acamera at one end of the vehicle and a test pattern at the other;

FIG. 2 is an elevation of the test pattern;

FIG. 3 is a schematic block diagram of the method of viewing andenhancing images already recorded on a camera;

FIGS. 4 a and 4 b are schematic diagrams showing the use of avectorscope, in correcting the colour and grayscale reproduction of apreviously recorded image containing a test pattern, (FIG. 4 a before),by electronically moving the signals from the test pattern into theirrespective vectorscope boxes, (FIG. 4 b after );

FIG. 5 is a schemaic illustration of advertising image incorporating atest pattern;

FIG. 6 is a schematic diagram showing the use of a moveable camera andseveral test patterns.

DESCRIPTION OF A SPECIFIC EMBODIMENT

As shown in FIG. 1 the invention is illustrated there as being installedin a bus or coach vehicle. It might, however, represent installations ina wide variety of locations, such as automobiles, cabs, trains, subways,airports, public spaces, platforms, aircraft, ships, hospitals, schools,highways, intersections and of course retail stores and commercial andoffice buildings, and in casinos.

Conceivably the system would find use in home security systems as well.Outdoor locations are not to be excluded, where such a system findsutility.

The security system consists of a camera (10) which is a typicalsecurity camera taking, usually video pictures, or in some cases aseries of stills, of the space to be surveyed.

Cameras of this type are well known, and are of great variety. They maybe provided with re-writable active memory (RAM), or image storage inthe form of a continuous roll of video tape, or a digital disc, or maybe connected to a larger system in which the pictures are recorded at aremote location.

Typically they will be focussed so as to record events and personsanywhere within the space. In larger spaces such cameras may be swung toand fro by remote control. In other cases there may be multiple camerasall taking pictures at the same time or one after the other.

The illustration of the one fixed camera is purely illustrative and isdeemed to include any and all such installations.

A test pattern (12) is shown mounted in a suitable location, within thefield of view of the camera. In this case it is at the end of the bus.

If the camera was of the moveable type, swinging to and fro across awider arc, then there may be several such test patterns, located atspaced apart locations.

The test pattern (12) consists of a series of test elements (14) and(16), (FIG. 2). These elements are formed with predetermined referencevalues.

Some elements (14) are “colour reference” elements. Other elements (16)are “grayscale reference” elements.

The colour elements (14) are based on the colour characteristics of thevideo or other system and they represent the hues of the primary andsecondary colours.

The values of the colours for an NTSC system based on a 2° observer atilluminant D65 are: Red=X32.1, Y23.2, Z15.1,-Green=X29.5, Y47.3,Z19.9-Blue=X21.0, Y16.5, Z59.7-Cyan=X38.2, Y50.7, Z65.4-Magenta=X40.8,Y26.7, Z60.6-Yellow=X49.3, Y57.5, Z20.8. Tolerance values are based onthe electronic reproduction of the pattern and are ±10 mV.

Other useful colours such as skin tones may also be included with thecolour elements (14).

The grayscale elements (16) are designed to be spectrophotometricallyneutral, reflecting red, green and blue light essentially equally, butat different brightness levels. The reflectance values for a seven stepgrayscale are: step 1=90%-step 2=63.6%-step 3=42.2%-step 4=25.5%-step5=13.2%-step 6=5.2%-step 7=1.0%. Tolerance varies from ±4% of step aimvalue at step 1 to 10% of step aim value at step 7.

The reflectivity of the grayscale elements (16) will vary from onegrayscale step or element to the next increasing in density from whiteto black white.

The camera will record the test pattern (12) any time the camera isrecording the scene, in this case in the bus. Thus both any activity inthe site, in the view field of the camera, will be recorded by thecamera, and at the same time the test pattern will also be recorded.

The scene may vary widely in clarity, ambient lighting and so on,resulting in inaccuracies when the images are reproduced later.

The persons or events in the images may also vary widely in definition,pigmentation, clothing and the like.

Since the test pattern has also been recorded at the same time andplace, it becomes possible to use the test pattern images to adjust thecharacteristics of the images of said scene, in the following manner.

Method of Operation.

When viewing images of the scene taken by the camera, the image of thetest pattern (12) enables corrections and adjustments to be made tooptimise the quality of the image of the scene.

When reproduction is inaccurate, as it will be in most cases, thenadjustment is required, to render the reproduction of the test patternmore accurate.

When these adjustments are made, the image of the test pattern isreproduced accurately. The color and grayscale elements will produceelectronic signals that fall at prescribed locations on measuringequipment well-known to the trade, such as vectorscopes and waveformmonitors. This therefore results in appropriate adjustment in the imagesof the scene.

A vectorscope used in video, displays Hue and colour Saturationinformation. A black and white signal from a camera, having no colourinformation produces a dot in the centre of the screen. The Huecomponent (red, green, blue etc) is defined by the angle of the signalfrom the centre. Relative to a clock face Red is approximately 11.30,Magenta about 1.30, Blue about 3.30, Green about 5.30, Cyan 7.00 andYellow 9.30. As colour saturation increases, the signal moves out fromthe centre of the screen, maximum colour saturation moves the signal tothe edge of the screen. Of the three components of a colour, Hue,Saturation and Brightness, a vectorscope displays only Hue andSaturation; Brightness must be viewed on a Waveform monitor capable ofindividually displaying the brightness of the Red, Green and Bluecomponents of a colour.

Before measuring pre-recorded or other video signals, a vectorscope'scalibration is checked using a precise electronically generated signalwith standard colour saturation amplitude of 75%. While looking at theelectronic signal on the vectorscope screen, the variable gain(amplification) control on the vectorscope is adjusted to position theRed, Green, Blue, Cyan, Magenta and Yellow signals in their respectiveboxes in the vectorscope graticule.

The pre-recorded test pattern image of the colour and grayscale areasshot with the camera is played back through a computer, or otherequipment capable of modifying the colour and tonal characteristics ofthe signal, while the image is viewed on a picture monitor and theelectronic signals are displayed on the vectorscope and/or waveformmonitor.

Because colours equivalent to the 75% electronic colour bar colours areseldom seen in real life, the saturation levels used in the test patterncolour elements are 50% lower than the 75% electronic colour barcolours, ±1%, at levels more representative of real life images. Coloursat this level of saturation will fall half way between the centre whitepoint of the vectorscope display and the 75% boxes for the respectivecolours. Adjusting the variable gain on a vectorscope by a factor of X2will, on a camera that is reproducing colour accurately, place the testpattern colour elements in their respective boxes.

For cameras that have not reproduced colours accurately, a computer, orother equipment capable of modifying the colour and tonalcharacteristics of the signal, is used to modify the colourcharacteristics to position the test pattern colour elements in theirrespective boxes. These colour correction settings may then be used tocorrect other images photographed using the same camera under similarlighting and exposure conditions, but without the test pattern being inthe scene.

Because vectorscopes only provide Hue and Saturation information,Brightness, the third and, an important component of colour, is omitted.The present system addresses this issue by incorporating specific Red,Green and Blue brightness level combinations of 551.25 mV and 288.75 mV±2.5% into each of the Red, Green, Blue, Cyan, Magenta and Yellowprimary colour elements of the test pattern.

For example, the R,G,B voltage levels produced by the Red colour elementare Red 551.25 mV, Green 288.75 mV and Blue 288.75 mV, the Cyan colourelement produces levels of Red 288.75 mV, Green 551.25 mV and Blue551.25 mV, other colour elements reproduce at similar combinations. Thisenables not only the Hue and Saturation, but also the Brightnesscomponent of colour images containing the test pattern to be corrected,or adjusted for a particular colour bias, using a voltage measuringdevice such as a three channel waveform monitor

Because the test pattern is illuminated by the same light source as therest of the scene, other elements within the scene will then also bereproduced accurately. Because test patterns change with age thepreferred embodiment would include a recommended replacement date withinthe active area of the test pattern. In another embodiment thesignificant test pattern information, such as precision grayscales andcolor elements and resolution information, would be disguised ingraphics such as public service announcements or even commercialadvertisements. An example of such a combination, essentially concealingthe test pattern (14) within a advertisement (18 ) as shown in FIG. 5.

It will be self evident that the system can also be applied to amoveable camera, as shown in FIG. 6. These cameras typically move fromone position to another in a series of steps.

By locating test patterns in the filed of the camera at each of the steppositions, any images recorded at any of the steps, will also containimages of the test pattern.

The foregoing is a description of a preferred embodiment of theinvention which is given here by way of example only. The invention isnot to be taken as limited to any of the specific features as described,but comprehends all such variations thereof as come within the scope ofthe appended claims.

What is claimed is:
 1. A security camera system mounted for recordingevents at a predetermined site, and comprising a security camera mountedand operable to record events within the filed of view of said camera atsaid site; a test pattern mounted at said site in said field of view ofsaid camera, said test pattern having precision color and grayscaleelements, having predetermined known spectrophotometrical values,whereby images taken at said site will contain images of said testpattern, thereby enabling adjustment of said images taken at said site,at a time subsequent to the actual taking of such images, to conformwith said predetermined known spectrophotometrical values.
 2. A securitycamera system as claimed in claim 1 in which the grayscale and colourelements are disguised in the form of a graphic message.
 3. A securitycamera system as claimed in claim 2, wherein said camera is moveablebetween at least two view stations, and including a said test pattern inthe field of view of said camera at each station.
 4. A security camerasystem as claimed in claim 2 wherein said test pattern has colourelements representing combinations of red, green and blue in thefollowing ranges. Red=X32.1, Y23.2, Z15.1,-Green=X29.5, Y47.3,Z19.9-Blue=X21.0, Y16.5, Z59.7 And having tolerance values of ±10 mV. 5.A security camera system as claimed in claim 4 wherein said test patternhas colour elements as aforesaid and further incorporating cyan,magenta, and yellow in the following ranges: Cyan=X38.2, Y50.7,Z65.4-Magenta=X40.8, Y26.7, Z60.6-Yellow=X49.3, 6, and having tolerancevalues of ±10 mV
 6. A security camera system as claimed in claim 4wherein said test pattern has grayscale elements as aforesaid which aredesigned to be spectrophotometrically neutral, reflecting red, green andblue light essentially equally, but at different brightness levels, andhaving reflectance values for a grayscale having seven stepped elementswhich are: step 1=90%-step 2=63.6%-step 3=42.2%-step 4=25.5%-step5=13.2%-step step 6=5.2%-step 7=1.0%, and having tolerance varying from±4% of step aim value at step 1 to ±10% of step aim value at step 7.wherein said series of elements have progressively increasing density.7. A security camera system as claimed in claim 4 wherein said camera ismounted on a moveable mount, power operated to move between a pluralityof stations, and including a said test pattern in the field of view ofsaid camera at each said station.
 8. A security camera system as claimedin claim 5 wherein wherein said camera is mounted on a moveable mount,power operated to move between a plurality of stations, and including asaid test pattern in the field of view of said camera at each saidstation.
 9. A security camera system as claimed in claim 6 whereinwherein said camera is mounted on a moveable mount, power operated tomove between a plurality of stations, and including a said test patternin the field of view of said camera at each said station.
 10. A methodof recording images at a site, and subsequently enhancing those imagesfor accuracy of reproduction and comprising the steps of; positioning atest pattern containing precision color elements having knownpredetermined spectrophotometrical values, and havingspectrophotometrically neutral grayscale elements, within the field ofview of said camera at said site; recording a scene including said testpattern within said camera's field of view; viewing recorded imagesthrough a system capable of adjusting image colour characteristics, saidsystem having at least a vectorscope for displaying colour hue andsaturation characteristics of said pattern image; and, adjusting imagecolour characteristics to position at least Red, Green, Blue, primarycolour areas in respective appropriate locations in the vectorscopedisplay.
 11. The method as claimed in claim 10 wherein said primarycolours further include Cyan, Magenta and Yellow.
 12. The method asclaimed in claim 11 wherein said primary colours include red, green andblue in the following ranges. Red=X32.1, Y23.2, Z15.1,-Green=X29.5,Y47.3, Z19.9-Blue=X21.0, Y16.5, Z59.7, and cyan, magenta, and yellow inthe following ranges: Cyan=X38.2, Y50.7, Z65.4-Magenta=X40.8, Y26.7,Z60.6-Yellow=X49.3, 6, and having tolerance values of ±10 mV.
 13. Themethod as claimed in claim 10 wherein said neutral grayscale elementsare designed to be spectrophotometrically neutral, reflecting red, greenand blue light essentially equally, but at different brightness levels,and having reflectance values for a grayscale having seven steppedelements which are: step 1=90%-step 2=63.6%-step 3=42.2%-step4=25.5%-step 5=13.2%-step 6=5.2%-step 7=1.0%, and having tolerancevarying from ±4% of step aim value at step 1 to ±10% of step aim valueat step
 7. wherein said series of elements have progressively increasingdensity.
 14. The method as claimed in claim 13 and further including thestep of adjusting image grayscale values to optimize the signal levelsand neutrality of said grayscale thereby correcting the same said valuesin said images of said scene.
 15. The method as claimed in claim 10, inwhich the grayscale and colour elements are disguised in the form of agraphic message.
 16. The method as claimed in claim 11, wherein saidcamera is moveable between at least two view stations, and including asaid test pattern in the field of view of said camera at each saidstation, and recording scenes at said stations of said site, andsimultaneously recording images of said test pattern at said respectivestation.